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Our future, our universe, and other weighty topics

Thursday, April 7, 2016

Cosmic Habitability Categories: Four Types of Universes

When we hear scientists
talk about different types of universes, they are usually talking
about the spatial geometry of the universe, and distinguish between a
flat universe, an open universe and a closed universe. But there is
another very interesting way to classify universes. We can classify
universes based not on their geometry but on their habitability –
how easy it is for life to develop in a universe. We can distinguish between
universes that are abundantly habitable, moderately habitable, barely
habitable and uninhabitable.

Before presenting such a
classification, let's look at two types of things that can contribute
to a universe's habitability. The first type of thing is what can be
called habitability necessities – things that a universe
must have in order for any life to exist in it. The second type of
thing is what can be called habitability boosters. By
“habitability boosters” I mean things that are not absolutely
necessary for any type of life to exist in a universe, but things which will tend to make
life more common and prevalent and long-lasting if they exist in a universe.

The Main Habitability
Necessities

Let's
look at some habitability necessities – things that absolutely must
be present for any advanced life to exist in a universe.

One
habitability necessity is stable atoms heavier than hydrogen, atoms
such as carbon and oxygen. We take stable atoms for granted, but
quite a few things have to go right in order for them to be possible. In
order for you to have elements other than hydrogen, you need to have
a strong nuclear force that binds protons together in the nucleus.
Such a force must be very strong to overcome the electromagnetic
repulsion between protons (all particles with the same charge repel
each other). Another requirement of stable atoms other than hydrogen
is an electromagnetic force, which keeps electrons orbiting around
the nucleus of the atom. If you don't have such a force, or if
electrons and protons have the same type of charge (both positive or
both negative), or if the electron charge differs greatly from the
proton charge, you cannot have atoms such as oxygen atoms and carbon
atoms. Another requirement for stable atoms and stable molecules are
certain quantum mechanical laws such as the Pauli exclusion
principle. As mentioned here, if there were no Pauli exclusion
principle there would be no chemistry.

Another
habitability necessity is the existence of large bodies such as
planets, with moderate levels of gravity on their surface. This
requires a universal force such as gravitation. This force must be
strong enough to hold planets together, but not so strong that
organisms living on the planet have to endure a crushing force that
always keeps them pinned in the same place on the ground. So a
habitable universe needs not just a universal force of gravitation,
but one that is neither too large nor small.

Another
habitability necessity is a relatively empty vacuum. By this I simply
mean a vacuum that has less mass-energy than solid steel. This is
something we take for granted, but (as discussed here) there are physics considerations
that imply such a thing should be incredibly unlikely. Strangely,
quantum field theory predicts that there should be all kinds of
quantum contributions to the vacuum that should cause it to be
incredibly dense with mass-energy. This is an unresolved problem of
physics known as the cosmological constant problem or the “vacuum
catastrophe” problem.

Another
habitability necessity is the existence of both carbon and oxygen in
adequate amounts. As far as we know, life could not exist without
either one. When physicists imagine universes with greatly different
physics, particularly a strong nuclear force much stronger or weaker,
it often means a universe with lots of carbon and no oxygen, or lots
of oxygen and no carbon.

This
is not a complete list of habitability necessities, but is enough to
clarify the concept.

The Main Habitability
Boosters

Now
let's look at some habitability boosters – things that are not
absolutely necessary for life to exist in a universe, but things that will tend to make
life much more widespread and long-lasting if they do exist. The
first habitability luxury I can think of is radiant stars – stars
that produce light and heat.

It
may surprise you that I have classified radiant stars as a
habitability booster rather than a habitability necessity. How could
life exist without stars? But the benefit that stars or suns supply
is light and heat, and a planet might have light and heart without
any radiant star near by. Volcanic activity, geological activity and
tidal effects can produce light and heat, such as we see on Jupiter's
moon Io.

We
can actually imagine intelligent life evolving on a small number of
planets in a universe that had no radiant stars. It would require a
rare type of planet which had volcanic activity or geological
activity or tidal activity that consistently produced heat and light
over many millions or billions of years. Even though there would be
probably less than one planet in a thousand that would have such
characteristics, there would still be quite a few such planets in a
universe with trillions of planets.

But
it could be argued that such planets could not exist, because carbon
and oxygen are formed in radiant stars. However, even if there were
no radiant stars there would probably be rare. freak events that
would cause carbon and oxygen to be created in rare spots – events
such as collisions of large astronomical bodies.

It
has been estimated that the total number of stars in the observable
universe is something like 10 to the twenty ninth power. Let's
imagine an alternate universe in which heavy elements such as carbon
and oxygen only form from freak events such as collisions of large
astronomical bodies. That would still leave you with trillions of planets
that might have heavy elements such as oxygen and carbon. If you
then imagine no radiant stars, and life only forming on planets that
gave off heat and light through geological activity, you would still
have a few hundred, thousand or million such planets (possibly even billions).

So we
must classify radiant stars as a habitability booster rather than a
habitability necessity. There is a related thing that we can
classify as a stronger and more specific habitability booster: the
existence of sun-like stars. It is believed that intelligent life
might evolve on planets revolving around small red stars. But it is
believed that if a planet existed in the habitable zone of a red
dwarf star, the planet would be so close to the star that it would
keep the same side pointed towards the star, without rotation. This
would probably limit life to existing in a ring-like area of the planet, between the
side facing the star, and the side facing away from it. If a universe
has not just red dwarf stars but also sun-like stars, it will tend to
be more habitable, with more life (all other things being equal). Planets revolving around sun-like stars can have life existing all over them, not just in a narrow ring between the front and the back of the planet.

Another
thing that must be classified as a habitability booster is the
presence of large amounts of both carbon and oxygen. Having lots of
carbon and oxygen around may be necessary for a universe with a huge
amount of life. But for a universe to be barely habitable, with only
a tiny amount of life, it needs only to have a few lucky spots where
there is a decent amount of carbon and oxygen.

Another
thing we can list as a habitability booster is low radioactivity. In
our universe radioactivity has a negligible effect on habitability,
because only rare very heavy elements such as uranium are
radioactive. But we can imagine a universe in which the strong
nuclear force was much weaker. In that case most elements would be
radioactive. The effect would probably be that creatures such as
us could not live longer than about 20 or 25 years before dying of
cancer caused by radioactivity.

Another
thing we can list as a habitability booster is low radiation from
sources such as gamma ray blasts and supernova explosions. We can
easily imagine a universe a little different in which there would be
a high chance of any newly evolved intelligent species being wiped
out by gamma ray blasts or supernova explosions, within a few million
years of when it appeared.

Another
thing we can list as a habitability booster is a low static
electricity. This is something that we take for granted, but which
is extremely unlikely in random universes. We have low amounts of
static electricity because the number of protons in the solar system
is roughly equal to the number of electrons, and the charge on the
proton (1836 times more massive than the electron) is the exact
opposite of the charge on the electron. But if such coincidences did
not exist, we might live on a planet that was teeming with local
charge imbalances -- lethal concentrations of static electricity. On such a planet it might be very common for
organisms to be killed when a creature simply stepped on a rock with
enough excess electrons to cause a lethal shock.

Four Types of Universes

Having
listed these types of habitability necessities and habitability
boosters, it is now easy to categorize four types of universes. They
are as follows:

Uninhabitable
universe: A universe in which intelligent life cannot evolve
anywhere, because it is missing one or more of the habitability
necessities.

Barely
habitable universe: A universe that has all of the habitability
necessities, but none or only one or two of the habitability
boosters.

Moderately
habitable universe: A universe that has all of the habitability
necessities, and roughly half of the habitability boosters.

Abundantly
habitable universe: A universe that has all of the habitability
necessities, and all or almost all of the habitability boosters.

Let's
imagine some universes, and then classify them as belonging to these
four types.

Universe 1: There are no sun-like stars, but many red dwarf stars. In
almost all solar systems in which a life-bearing planet revolves
around a red dwarf star, the planet keeps the same side always
pointing toward the star, and life exists in a narrow band between
that side and the other side of the planet. There's also a lot more
gamma ray bursts than in our universe.

What
type of universe is this? It seems like a moderately habitable
universe.

Universe 2: There are no radiant stars at all, and the night sky always
looks dark. Carbon and oxygen are rare. But in certain rare places
some freak events such as astronomical collisions led to local
abundances of carbon and oxygen that eventually became planets. In a
small number of these planets, special geological conditions created
enough light and heat for intelligent life to evolve. But the future
prospects are dim for such life forms, since a change in geological
conditions might deprive them of the heat and light they need.

What
type of universe is this? It seems like a barely habitable universe.

Universe 3: There are radiant stars, and countless stable planets. There
are not just red stars, but also stars like the sun. There are no
habitability factors that should limit the universe from having
trillions of planets bearing intelligent life. Planets typically
enjoy low amounts of harmful radiation, low radioactivity, and low
amounts of static electricity. There are trillions of planets on
which nothing physical prevents intelligent life from existing for
billions of years.

Which
type of universe is this? It's an abundantly habitable universe.

Which
type of universe do we live in? Each of the habitability boosters I
previously listed are conditions of our universe. And obviously our
universe has all of the habitability necessities, or we wouldn't
exist. So we must classify our universe as an abundantly habitable
universe.

Recent
news stories bolster this conclusion. A significant fraction of the
universe's galaxies are rather spherical-shaped elliptical galaxies
different from our own spiral galaxy. It used to be believed that elliptical
galaxies must be lifeless, because of a lack of heavy elements. But
recently scientists concluded that large elliptical galaxies can
produce up to 10,000 times as many Earth-like planets as our galaxy.
It seems, in fact, that all of the three major types of galaxies in
our universe (spiral, irregular, and elliptical) can support planets
with life. The Kepler telescope has helped confirm that there are planets all over the place in our galaxy. We know of very few or
no habitability shortfalls in our universe, so it must be classified
as abundantly habitable.

But
what type of universe should we expect our universe to be? This is a
fascinating question with some interesting philosophical
implications. In my next post I will discuss this question,
discussing the relative probabilities of getting the types of
universes I have listed. I will show that conventional assumptions like those made
by most scientists lead to shockingly erroneous predictions about the type of universe our universe should be.

As I will show in my next post, without the cheat of assuming there must be an observer, such assumptions lead to the prediction that our universe should be uninhabitable. Even if one makes such a cheat, by assuming an observer, such assumptions lead to the prediction that we should live in a barely habitable universe much, much less favorable to life than the one we live in.

Copyright Notice

All posts on this blog are authored by Mark Mahin, and are protected by copyright. Copyright 2013-2014 by Mark Mahin. All rights reserved. Any resemblance between any fictional character and any real person is purely coincidental.